CHAPTER 2-1

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CHAPTER 2-1

ATOMS

Atom – is the basic unit of matter

Ex. Democritus – breaking a piece of chalk, when is it not chalk anymore? Until atomos “unable to be cut”

An atom is very small. 100 million atoms make up about 1 cm.

ATOMS

Atoms are made of smaller subatomic particles: protons, neutrons and electrons.

Protons have a positive charge, neutrons a neutral charge and together they make up the nucleus of an atom

Electrons are negatively charged and much smaller than protons

Atoms have a neutral charge, equal number of electrons and protons

ELEMENT

An element is a pure substance made up of just one type of atom

Elements have a one or two letter symbol

The number of protons equals the atomic number of the element

ELEMENT

Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.

Isotopes are identified by their mass number

Isotopes of an element are similar because they have the same number of electrons; all isotopes of an element have the same chemical properties.

Radioactive isotopes are important to use for dating and labels to follow the movement of substances within organisms.

CHEMICAL COMPOUNDS

A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.

Written in shorthand known as a chemical formula

CHEMICAL COMPOUNDS

The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed.

Ex. Sodium Chloride – Sodium and Chlorine

CHEMICAL BONDS

The main types of chemical bonds are ionic bonds and covalent bonds.

An ionic bond is formed when one or more electrons are transferred from one atom to another.

Positively and negatively charge atoms are known as

ions.

CHEMICAL BONDS

A covalent bond is formed when one or more pairs of electrons are shared between two atoms.

Can be a single, double or triple bond

CHEMICAL BONDS

A molecule is the smallest unit of most compounds.

Ex. Water – H2O

Doesn’t usually share electrons equally between the two atoms

CHEMICAL COMPOUNDS

Van der Waals forces are a type of intermolecular interaction in which when molecules are close together, a slight attraction develops between the oppositely charge regions of nearby molecules.

Ex. Tokay gecko

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